If you can and are willing to carry the financial weight then that's fine I guess. Only thing I would be concerned is how her temper plays into wanting to live beyond her means. I bring this up because of the comment you made about wanting an expensive wedding and being impulsive.
If her temper and inability to solve problems without fighting can be a consequence of not being able to get something you can't always provide right away financially or just not in the best interest of the overall family then that might be an issue.
edit : this is what I was referring to
She knows what she wants and she wants it. If she needs thirty minutes to get ready and four people are waiting on her, she needs thirty minutes. If she wants to lease a new car and it doesn't make financial sense, but she thinks she it will be safer for her, she will lease it. She doesn't think of other people's rights or what's fair, she focuses on what she wants.
This sounds like immaturity to me. What happens if she wants something right now but you need 30 minutes to finish something important? What if she really wants something that you know from a logical and rational standpoint will fix her short term gratification needs but will come bite her (and you) in the ass in the long term?
I guess what I am simply saying is to make sure she has realistic expectations and also that she can work on her temper and issues that are important to you. Hope it works out for you.